Q: What does a Power Supply do? Why buy a Power Supply?A: A power supply is a device that supplies regulated power to an electronic device like your computer or printer. Often times a power supply is used to adapt the available voltage and current to levels that are more suitable to the device it is powering. For example an AC power supply might take your plug-in wall voltage and drop it from 110 volts AC to 9 volts AC in order to power a phone charger. Power inverters that change DC voltage to AC voltage are also sometimes referred to as power supplies. These units allow you to run many plug-in AC devices like chargers, small appliances and TVs off of your car's 12 volt DC system.